The present invention relates to a battery wherein a battery cover and a safety valve are overlapped at an open part of a battery case internally housing a power generation component.
In recent years, many portable electronic devices such as a mobile phone, a combination camera (video tape recorder), and a laptop computer have been introduced. Improvement in performance of these portable electronic devices has been aspired. Along with these situations, improvement in energy density, downsizing, and weight saving of a secondary battery coverable of being charged and discharged as a power source for the portable electronic device have been aspired. Specially, a lithium ion secondary battery is superior in the respect that the lithium ion secondary battery has higher energy and can be used for a longer time than a lead battery, a nickel cadmium battery and the like.
Conventionally, in order to house a power generation component, a metal battery case has been widely used for the lithium ion secondary battery. FIG. 1 shows a view which enlarges part of a battery using the metal battery case. In this battery, a power generation component 120 sandwiched between a pair of insulating plates 130 is housed inside a battery case 110. Battery covers 140 and a safety mechanism 150 provided inside the battery cover 140 are installed to an open part of the battery case 110 by caulking through a gasket 160. A safety valve 151 transformed by a given pressure is provided for the safety mechanism 150 so that the safety valve 151 is overlapped with the battery cover 140. A cathode lead 121 derived from the power generation component 120 is connected to the safety valve 151 through a contact plate 152. The battery cover 140 and the power generation component 120 are thereby electrically connected.
In such a battery wherein the battery cover 140 and the safety valve 151 are simply overlapped, however, there has been a problem that when temperature change or mechanical shock is applied, a contact resistance between the battery cover 140 and the safety valve 151 is increased, leading to increase in an internal resistance.
Therefore, as shown in FIG. 2, actions have been taken, for example, an outer periphery part of a flange part 141 of the battery cover 140, which contacts with the safety valve 151 is bent toward the safety valve 151 side (refer to Japanese Unexamined Patent Application Publication No. 2001-126682).
In the foregoing example, however, there has been a problem that process automation is difficult since when an automated machine is used in a manufacturing process, troubles may arise, for example, parts are not carried smoothly, or a carriage jig or the like is shaved by a bent part of the battery cover 140.